I. General Detection Systems and the Problem
Infrared imaging or detection is anticipated to be a useful aid in the diagnosis and management of various diseases or clinical pathologies indicated by temperature variations of the skin. For example, it is thought that infrared detection and assessment of true skin temperature may be an important diagnostic and curative tool in the treatment of malignancies, burns, wounds to the skin and also, to measure and perfect the use of topical treatments absorbed through the skin.
On account of the characteristics of the skin and the strict requirements of accurate measurement of absolute skin temperature for diagnosis and management, a relatively artifact-free system is needed to detect and measure the key parameters for effective clinical application of the concept; i.e., accurate measurement of absolute skin temperature, emissivity and fluorescence.
The currently available infrared imaging and sensing systems adaptable for clinical use, both economically and scientifically, typically measure infrared flux over a single band of the infrared spectrum somewhere between 8 and 12 .mu.m. These systems estimate the temperature of an image (e.g., an area of interest on the skin) by comparing the amount of infrared flux detected with that emitted by an ideal "black body" emitter at a known temperature. This technique assumes, of course, that the skin, in the 10 .mu.m range, is not reflective (or fluorescent) and accordingly, has an emissivity equal to that of an ideal "black body."
This is clearly not the case. Skin emissivity is somewhat less than 100% in a normal state, and the skin can become even more reflective if treated with topical agents or if exposed to extraneous light or other environmental conditions. In addition, conditions exist where the skin becomes fluorescent thereby emitting infrared flux in excess of that of an ideal "black body" at a specific wavelength.
The skin, as well as being affected by topical agents or disease, also changes spectral characteristics through interaction with visible and infrared radiation from other sources in the clinical laboratory or surrounding clinical environment. Accordingly, still further aberrations occur in the "black body" comparison now used to estimate skin temperature.
On account of these aberrations, the "black body" comparison is inadequate for medical diagnosis and management. In addition, single parameter corrections of skin temperature are also not appropriate since the reflectivity of the skin is wavelength dependent unlike that of the "gray body." Further, reflectivity of the skin is associated with artifacts related to environmental infrared emissions.
It is important, therefore, to determine absolute temperature, fluorescence and emissivity (or reflectivity) because these parameters and the relationships among them may be quantifiable and related to certain pathologies or important clinical applications. In short, if one can accurately measure of fluorescence and reflectivity in the infrared 10 .mu.m band, one can then accurately calculate and assess temperature through the use of a corrected "black body" calculation and comparison.